John Gill Commentary 1 Samuel 26:25

"Then Saul said to David, Blessed be thou, my son David: thou shalt both do mightily, and shalt surely prevail. So David went his way, and Saul returned to his place." — 1 Samuel 26:25 (ASV)

Then Saul said to David, blessed [be] you, my son David
He desired God to bless him, and pronounced him blessed himself, believing he would be a happy and prosperous man:

you shall both do great [things] ;
he had done great things already, in slaying Goliath, obtaining victories over the Philistines, and escaping the hands of Saul, and keeping out of them with so small a force; and he should do greater things yet:

and also shall still prevail ;
against Saul and all his enemies; the Targum is, ``even in reigning you shall reign, and even in prospering you shall prosper;'' he believed he would be king, so he had said before, (1 Samuel 24:20) ;

so David went on his way :
to the wilderness again very probably, putting no trust and confidence in Saul, knowing how fickle and unstable he was:

and Saul returned to his place ;
to Gibeah, where his palace was.